Zinc ions regulate opening of tight junction favouring efflux of macromolecules via the GSK3β/snail-mediated pathway

Zinc alleviates thermal stress-induced damage to the integrity and barrier function of cultured chicken embryonic primary jejunal epithelial cells via the MAPK and PI3K/AKT/mTOR signaling pathways

Zinc (Zn) could alleviate the adverse effect of high temperature (HT) on intestinal integrity and barrier function of broilers, but the underlying mechanisms remain unclear. We aimed to investigate the possible protective mechanisms of Zn on primary cultured broiler jejunal epithelial cells exposed to thermal stress (TS). In Exp.1, jejunal epithelial cells were exposed to 40℃ (normal temperature, NT) and 44℃ (HT) for 1, 2, 4, 6, or 8 h. Cells incubated for 8 h had the lowest transepithelial resistance (TEER) and the highest phenol red permeability under HT. In Exp.2, the cells were preincubated with different Zn sources (Zn sulfate as iZn and Zn proteinate with the moderate chelation strength as oZn) and Zn supplemental levels (50 and 100 µmol/L) under NT for 24 h, and then continuously incubated under HT for another 8 h. TS increased phenol red permeability, lactate dehydrogenase (LDH) activity and p-PKC/PKC level, and decreased TEER, cell proliferation, mRNA levels of claudin-1, occludin, zona occludens-1 (ZO-1), PI3K, AKT and mTOR, protein levels of claudin-1, ZO-1 and junctional adhesion molecule-A (JAM-A), and the levels of p-ERK/ERK, p-PI3K/PI3K and p-AKT/AKT. Under HT, oZn was more effective than iZn in increasing TEER, occludin, ZO-1, PI3K, and AKT mRNA levels, ZO-1 protein level, and p-AKT/AKT level; supplementation with 50 μmol Zn/L was more effective than 100 μmol Zn/L in increasing cell proliferation, JAM-A, PI3K, AKT, and PKC mRNA levels, JAM-A protein level, and the levels of p-ERK/ERK and p-PI3K/PI3K; furthermore, supplementation with 50 μmol Zn/L as oZn had the lowest LDH activity, and the highest ERK, JNK-1, and mTOR mRNA levels. Therefore, supplemental Zn, especially 50 μmol Zn/L as oZn, could alleviate the TS-induced integrity and barrier function damage of broiler jejunal epithelial cells possibly by promoting cell proliferation and tight junction protein expression via the MAPK and PI3K/AKT/mTOR signaling pathways.

Cerebrospinal fluid efflux through dynamic paracellular pores on venules as a missing piece of the brain drainage system

The glymphatic system plays a key role in the clearance of waste from the parenchyma, and its dysfunction has been associated with the pathogenesis of Alzheimer's disease (AD). However, questions remain regarding its complete mechanisms. Here, we report that efflux of cerebrospinal fluid (CSF)/interstitial fluid (ISF) solutes occurs through a triphasic process that cannot be explained by the current model, but rather hints at the possibility of other, previously undiscovered routes from paravenous spaces to the blood. Using real-time, in vivo observation of efflux, a novel drainage pathway was discovered, in which CSF molecules enter the bloodstream directly through dynamically assembled, trumpet-shaped pores (basolateral ϕ<8 μm; apical ϕ < 2 μm) on the walls of brain venules. As Zn2+ could facilitate the brain clearance of macromolecular ISF solutes, Zn2+-induced reconstruction of the tight junctions (TJs) in vascular endothelial cells may participate in pore formation. Thus, an updated model for glymphatic clearance of brain metabolites and potential regulation is postulated. In addition, deficient clearance of Aβ through these asymmetric venule pores was observed in AD model mice, supporting the notion that impaired brain drainage function contributes to Aβ accumulation and pathogenic dilation of the perivascular space in AD.

Metal-organic framework materials promote neural differentiation of dental pulp stem cells in spinal cord injury

Spinal cord injury (SCI) is accompanied by loss of Zn2+, which is an important cause of glutamate excitotoxicity and death of local neurons as well as transplanted stem cells. Dental pulp stem cells (DPSCs) have the potential for neural differentiation and play an immunomodulatory role in the microenvironment, making them an ideal cell source for the repair of central nerve injury, including SCI. The zeolitic imidazolate framework 8 (ZIF-8) is usually used as a drug and gene delivery carrier, which can release Zn2+ sustainedly in acidic environment. However, the roles of ZIF-8 on neural differentiation of DPSCs and the effect of combined treatment on SCI have not been explored. ZIF-8-introduced DPSCs were loaded into gelatin methacryloyl (GelMA) hydrogel and in situ injected into the injured site of SCI rats. Under the effect of ZIF-8, axon number and axon length of DPSCs-differentiated neuro-like cells were significantly increased. In addition, ZIF-8 protected transplanted DPSCs from apoptosis in the damaged microenvironment. ZIF-8 promotes neural differentiation and angiogenesis of DPSCs by activating the Mitogen-activated protein kinase (MAPK) signaling pathway, which is a promising transport nanomaterial for nerve repair.

ZnUMBA - a live imaging method to detect local barrier breaches

Epithelial barrier function is commonly analyzed using transepithelial electrical resistance, which measures ion flux across a monolayer, or by adding traceable macromolecules and monitoring their passage across the monolayer. Although these methods measure changes in global barrier function, they lack the sensitivity needed to detect local or transient barrier breaches, and they do not reveal the location of barrier leaks. Therefore, we previously developed a method that we named the zinc-based ultrasensitive microscopic barrier assay (ZnUMBA), which overcomes these limitations, allowing for detection of local tight junction leaks with high spatiotemporal resolution. Here, we present expanded applications for ZnUMBA. ZnUMBA can be used in Xenopus embryos to measure the dynamics of barrier restoration and actin accumulation following laser injury. ZnUMBA can also be effectively utilized in developing zebrafish embryos as well as cultured monolayers of Madin-Darby canine kidney (MDCK) II epithelial cells. ZnUMBA is a powerful and flexible method that, with minimal optimization, can be applied to multiple systems to measure dynamic changes in barrier function with spatiotemporal precision.

Brain Region-Specific Differences in Amyloid-β Plaque Composition in 5XFAD Mice

Senile plaques consisting of amyloid-beta (Aβ) peptides are a major pathological hallmark of Alzheimer's disease (AD). Aβ peptides are heterogeneous regarding the exact length of their amino- and carboxy-termini. Aβ1-40 and Aβ1-42 are often considered to represent canonical "full-length" Aβ species. Using immunohistochemistry, we analyzed the distribution of Aβ1-x, Aβx-42 and Aβ4-x species in amyloid deposits in the subiculum, hippocampus and cortex in 5XFAD mice during aging. Overall plaque load increased in all three brain regions, with the subiculum being the area with the strongest relative plaque coverage. In the subiculum, but not in the other brain regions, the Aβ1-x load peaked at an age of five months and decreased thereafter. In contrast, the density of plaques positive for N-terminally truncated Aβ4-x species increased continuously over time. We hypothesize that ongoing plaque remodeling takes place, leading to a conversion of deposited Aβ1-x peptides into Aβ4-x peptides in brain regions with a high Aβ plaque burden.

Proton-Pump Inhibitors Suppress T Cell Response by Shifting Intracellular Zinc Distribution

Proton-pump inhibitors (PPI), e.g., omeprazole or pantoprazole, are the most widely used drugs for various gastrointestinal diseases. However, more and more side effects, especially an increased risk of infections, have been reported in recent years. The underlying mechanism has still not yet been fully uncovered. Hence, in this study, we analyzed the T cell response after treatment with pantoprazole in vitro. Pantoprazole preincubation reduced the production and secretion of interferon (IFN)-γ and interleukin (IL)-2 after the T cells were activated with phytohemagglutinin (PHA)-L or toxic shock syndrome toxin-1 (TSST-1). Moreover, a lower zinc concentration in the cytoplasm and a higher concentration in the lysosomes were observed in the pantoprazole-treated group compared to the untreated group. We also tested the expression of the zinc transporter Zrt- and Irt-like protein (Zip)8, which is located in the lysosomal membrane and plays a key role in regulating intracellular zinc distribution after T cell activation. Pantoprazole reduced the expression of Zip8. Furthermore, we measured the expression of cAMP-responsive element modulator (CREM) α, which directly suppresses the expression of IL-2, and the expression of the phosphorylated cAMP response element-binding protein (pCREB), which can promote the expression of IFN-γ. The expression of CREMα was dramatically increased, and different isoforms appeared, whereas the expression of pCREB was downregulated after the T cells were treated with pantoprazole. In conclusion, pantoprazole downregulates IFN-γ and IL-2 expression by regulating the expression of Zip8 and pCREB or CREMα, respectively.

Clearance Systems in the Brain, From Structure to Function

As the most metabolically active organ in the body, there is a recognized need for pathways that remove waste proteins and neurotoxins from the brain. Previous research has indicated potential associations between the clearance system in the brain and the pathological conditions of the central nervous system (CNS), due to its importance, which has attracted considerable attention recently. In the last decade, studies of the clearance system have been restricted to the glymphatic system. However, removal of toxic and catabolic waste by-products cannot be completed independently by the glymphatic system, while no known research or article has focused on a comprehensive overview of the structure and function of the clearance system. This thesis addresses a neglected aspect of linkage between the structural composition and main components as well as the role of neural cells throughout the clearance system, which found evidence that the components of CNS including the glymphatic system and the meningeal lymphatic system interact with a neural cell, such as astrocytes and microglia, to carry out vital clearance functions. As a result of this evidence that can contribute to a better understanding of the clearance system, suggestions were identified for further clinical intervention development of severe conditions caused by the accumulation of metabolic waste products and neurotoxins in the brain, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Zinc as a Neuroprotective Nutrient for COVID-19-Related Neuropsychiatric Manifestations: A Literature Review

The outbreak of the pandemic associated with Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) led researchers to find new potential treatments, including nonpharmacological molecules such as zinc (Zn2+). Specifically, the use of Zn2+ as a therapy for SARS-CoV-2 infection is based on several findings: 1) the possible role of the anti-inflammatory activity of Zn2+ on the aberrant inflammatory response triggered by COronaVIrus Disease 19 (COVID-19), 2) properties of Zn2+ in modulating the competitive balance between the host and the invading pathogens, and 3) the antiviral activity of Zn2+ on a number of pathogens, including coronaviruses. Furthermore, Zn2+ has been found to play a central role in regulating brain functioning and many disorders have been associated with Zn2+ deficiency, including neurodegenerative diseases, psychiatric disorders, and brain injuries. Within this context, we carried out a narrative review to provide an overview of the evidence relating to the effects of Zn2+ on the immune and nervous systems, and the therapeutic use of such micronutrients in both neurological and infective disorders, with the final goal of elucidating the possible use of Zn2+ as a preventive or therapeutic intervention in COVID-19. Overall, the results from the available evidence showed that, owing to its neuroprotective properties, Zn2+ supplementation could be effective not only on COVID-19-related symptoms but also on virus replication, as well as on COVID-19-related inflammation and neurological damage. However, further clinical trials evaluating the efficacy of Zn2+ as a nonpharmacological treatment of COVID-19 are required to achieve an overall improvement in outcome and prognosis.

General Aspects of Metal Ions as Signaling Agents in Health and Disease

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction-the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

The effects of zinc treatment on matrix metalloproteinases: A systematic review

BACKGROUND

Zinc (Zn) acts as a cofactor of matrix metalloproteinases (MMPs) and is vital for their activity and controlling their expression. Alteration of Zn in the body could affect the expression, activity, and destructive impacts of MMPs.

OBJECTIVE

This systematic review aimed to summarize existing evidence on the effects of Zn treatment on the expression and activity of MMPs.

METHOD

International sources from Pub Med, Scopus and Google Scholar were searched for the original and English-language studies, published up to the end of May 2018.

RESULTS

During the initial search, 179 records were found, and 135 articles of them remained after the exclusion of duplicate articles. 47 studies met the inclusion criteria, after multiple stages of screening and critical reviews of articles.

CONCLUSION

Approximately 62% of the included studies (29 of 47) showed an inhibitory impact of Zn on MMPs production and activities. The inhibitory or stimulatory effect of Zn on MMPs seems to depend on physiological conditions of the cells or animals used, dose of Zn used, and duration of treatment.

Biomaterial-tight junction interaction and potential impacts

The active pharmaceutical ingredients (APIs) have to cross the natural barriers and get into the blood to impart the pharmacological effects. The tight junctions (TJs) between the epithelial cells serve as the major selectively permeable barriers and control the paracellular transport of the majority of hydrophilic drugs, in particular, peptides and proteins. TJs perfectly balance the targeted transport and the exclusion of other unexpected pathogens under the normal conditions. Many biomaterials have shown the capability to open the TJs and improve the oral bioavailability and targeting efficacy of the APIs. Nevertheless, there is limited understanding of the biomaterial-TJ interactions. The opening of the TJs further poses the risk of autoimmune diseases and infections. This review article summarizes the most updated literature and presents insights into the TJ structure, the biomaterial-TJ interaction mechanism, the benefits and drawbacks of TJ disruption, and methods for evaluating such interactions.

Non-Dopaminergic Therapies

Currently all aspects of Parkinson’s disease (PD) treatment are less than ideal and would benefit from new interventions. We focus on problems associated with brain neurotransmitters amenable to more specific subreceptor and temporal manipulation. In addition, we consider potentially treatable CNS non-PD co-pathologies or co-morbidities that may exacerbate progression of various aspects of PD.

Rho Flares Repair Local Tight Junction Leaks

Tight junctions contribute to epithelial barrier function by selectively regulating the quantity and type of molecules that cross the paracellular barrier. Experimental approaches to evaluate the effectiveness of tight junctions are typically global, tissue-scale measures. Here, we introduce Zinc-based Ultrasensitive Microscopic Barrier Assay (ZnUMBA), which we used in Xenopus laevis embryos to visualize short-lived, local breaches in epithelial barrier function. These breaches, or leaks, occur as cell boundaries elongate, correspond to visible breaks in the tight junction, and are followed by transient localized Rho activation, or Rho flares. We discovered that Rho flares restore barrier function by driving concentration of tight junction proteins through actin polymerization and ROCK-mediated localized contraction of the cell boundary. We conclude that Rho flares constitute a damage control mechanism that reinstates barrier function when tight junctions become locally compromised because of normally occurring changes in cell shape and tissue tension.

The interaction of zinc and the blood-brain barrier under physiological and ischemic conditions

Zinc is the second most abundant metal in human and serves as an essential trace element in the body. During the past decades, zinc has been found to play important roles in central nervous system, such as the development of neurons and synaptic activities. An imbalance of zinc is associated with brain diseases. The blood-brain barrier (BBB) maintains the homeostasis of the microenvironment, regulating the balance of zinc in the brain. A compromised BBB is the main cause of severe complications in cerebral ischemic patients, such as hemorrhage transformation, inflammation and edema. Recent studies reported that zinc in the brain may be a potential target for integrative protection against ischemic brain injury. Although zinc has long been regarded as important transmitters in central nervous system, the critical role of zinc dyshomeostasis in damage to the BBB has not been fully recognized. In this review, we summarize the role of the BBB in regulating homeostasis of zinc in physiological conditions and the effects of changes in zinc levels on the permeability of the BBB in cerebral ischemia. The integrity of BBB maintains the homeostasis of zinc in pathological conditions, while the balance of zinc in the brain and the circulation maintains the normal function of the BBB. Interrupting the zinc/BBB system will disturb the microenvironment in the brain, leading to pathological diseases. In stroke patients, zinc may serve as a potential target for protecting the BBB and reducing hemorrhage transformation, inflammation and edema.